1. Field of the Invention
The present invention relates to a powder fabricating apparatus, more specifically, to a continuous powder fabricating apparatus by using a screw, wherein said apparatus can obtain metal powder easily and rapidly, in which the metal powder has an important position in the industrial field.
2. Description of the Related Art
Generally, metal powder, which is metal particle at a size less than 1,000 μm, is characterized by fluidity, mixability, compressibility, moldability, explosiveness, sintering and the like. The properties of the metal powder change according to not only its ingredient but also the size or shape of the particle. There are various kinds of metal powder such as iron, aluminum, copper, nickel, zinc, manganese, rare-earth elements, platinum group metals and rare metals.
Among them, rare-earth elements, which consist of 17 elements, lanthanum (La, atomic number 57) to lutetium (Lu, atomic number 71), scandium (Sc, atomic number 21) and yttrium (Y, atomic number 39), may become a metallic oxide that has a high melting point and is difficult to be reduced. The platinum group elements have a high melting point and are uneasily oxidizable, corrosive, noble metals, which are composed of 6 elements (ruthenium, rhodium, palladium, osmium, iridium and platinum) of Group 8 in the periodic table, not including the iron group. Rare metals (scarcity metals or minor metals) are necessary to support a high level of technology despite a low production scale. There are 3 classes of rare metals: the first class consists of silicon, sodium, manganese, potassium, calcium, titanium and the like, which are predominately found in the earth's crust though difficult to smelt; the second class consists of arsenic, bismuth, selenium, antimony, cadmium, cobalt, tellurium and the like, which are less likely to be found in the earth's crust although easy to smelt; the third class consists of germanium, niobium, lithium, molybdenum, barium, beryllium, boron, cerium, strontium, uranium, indium, zirconium, potassium, tantalum, thallium, wolfram, thorium, hafnium and the like, which are sparsely found in the earth's crust and difficult to smelt. The increasing demand for rare metals parallels the rapid development of the IT industry, particularly the electronics and communications fields.
Niobium (Nb) is characterized by a low-neutron absorbing sectional area, good ductility, oxidation-resistance, heat-resistance, impact-resistance and high transition temperature, and is widely used in the fields of nuclear fusion or nuclear power technology, space development, high electric power transmission and superconductors. Tantalum (Ta) has a high melting point and low vapor pressure, good ductility, mechanical strength and oxidation-resistance. As such, the demand for tantalum has dramatically increased in the electric, electronic and/or chemical industries. As indicated above, tantalum and niobium, which are generally used in materials of electronic components or agents for improving physical properties, have high melting points and high resistance for a chemical agent. Thus, a metal thermo-reducing method, in which K2TaF7 or K2NbF7 is a reactant and metals such as Na, K, Ca or Al are used when the powder (nano particle) is fabricated, has been employed.
Until now, batch-type metal powder fabricating apparatuses have been used. The conventional batch-type metal powder fabricating apparatus, as shown in FIG. 5, comprises a reactant supplier 100, a reaction bath 200, a mixer 300 for mixing the reactant supplied to the reaction bath 200 and a heater 500, which is mounted around the reaction bath 200 for heating the reaction bath 200. In the conventional batch-type metal powder fabricating apparatus, after a dose of the reactant is added into the reaction bath 200 through the reactant supplier 100, a dose of the product can be obtained by completing the reaction with the mixer 300 and the heater 500.
However, the conventional batch-type metal powder fabricating apparatus is inconvenient because it is difficult to analyze the reaction of the reactant, requires a long time for reaction and is large to guarantee productivity. Also, a reactant or reducing agent is gradually supplied in order to control reactant heat, or many diluents are supplied in order to control a reaction rate, which prolongs the reaction time. In addition, a diluent of high purity should be used to reduce a pollution source from the diluent. Since the diluent itself becomes reaction waste, it is also inefficient. Particularly, in the conventional batch-type or semi-batch type reactor, the overall reaction time or grain growth time is a very important factor in determining grain-size distribution because an average size of a first particle is determined by such grain growth time to the overall reaction rate. However, since such reactors depend solely on a time control method to control grain-size distribution, it is very difficult to obtain a product whose grain-size distribution is uniform.